FORAMINIFERA 69 



formed of siliceous plates secreted by the animal; pseudopodia filose. 

 In fresh waters. 



Trichosphaerium. Flat, encrusting forms, with a jelly coat; finger- 

 like pseudopodia protruding through separate openings in the coat; 

 and numerous nuclei. Reproduction alternately by escape of amoe- 

 bulae and of biflagellate isogametes ; but both generations can perform 

 plasmotomy. Marine. 



LieberkUhnia (Fig. 61) Shell thin, flexible, egg-shaped, with 

 mouth directed to one side; pseudopodia reticulate. Shell divided at 

 binary fission. Marine and in fresh waters. 



sh. 



Fig. 60. Fig. 61. 



Fig. 60. Difflugia urceolata, x 100. After Leidy. sh. shell composed of 

 particles of sand containing body of the animal ; ps. pseudopodia. 

 Fig. 61. Lieberkuhnia wagneri. After Verworn. 



Suborder POLYTHALAMIA 

 Foraminifera, nearly always of marine habitat ; usually with a shell 

 of several chambers, which is most often calcareous, but sometimes 

 with one chamber or no shell ; whose pseudopodia are reticulate ; and 

 whose protoplasm extends as a layer over the shell. 



The external layer of protoplasm can be withdrawn into the shell. 



The shells of this group are typically many-chambered and cal- 

 careous, but a fair number are one-chambered, and most of these and 

 some of the many-chambered shells are composed of foreign particles 

 (arenaceous). Either kind may be imperforate ox perforate by numerous 

 small pores, but most of the non-calcareous shells are imperforate. 

 The one-chambered shells are of various shapes. They usually grow 

 by extension at their openings. Shells with more than one chamber 



